Method for manufacturing liquid-cooling jacket and friction stir welding method

ABSTRACT

The present invention includes: a primary joining process in which a coarse portion having a predetermined width is formed in the vicinity of a step side face within a plasticized region while the rotary tool is being moved one round along a first butted portion to perform friction stirring in a state that a tip of a tip side pin of a rotary tool being rotated is inserted to the same depth as or slightly deeper than a step bottom face and an outer circumferential face of a base side pin is in contact with a front face of a sealing body and the tip side pin is slightly in contact with at least an upper portion of a jacket body and an inspection process in which a passed position of the tip side pin is specified by performing, a flaw detection to detect the coarse portion.

TECHNICAL FIELD

The present invention relates to a method for manufacturing aliquid-cooling jacket and a friction stir welding method.

BACKGROUND ART

A method for manufacturing a liquid-cooling jacket utilizing frictionstir welding is performed. For example, Patent Literature 1 discloses amethod for manufacturing a liquid-cooling jacket. FIG. 16 is a crosssectional view showing a conventional method for manufacturing aliquid-cooling jacket. In the conventional method for manufacturing aliquid-cooling jacket, friction stir welding is performed to a buttedportion J10 where a side face 102 c of a sealing body 102 made of analuminum alloy is butted against a step side face 101 c of a steppedportion of a jacket body 101 made of an aluminum alloy. Further, in theconventional method for manufacturing a liquid-cooling jacket, frictionstir welding is performed in a state that only a stirring pin FD2 of arotary tool FD is inserted in the butted portion J10. Furthermore, inthe conventional method for manufacturing a liquid-cooling jacket, therotary tool FD is relatively moved in a state that a rotation axis XA ofthe rotary tool FD overlaps with the butted portion J10.

CITATION LIST Patent Literature

Patent Literature 1: JP 2015-131321 A

SUMMARY OF INVENTION Technical Problem

In general, the jacket body 101 tends to have a complex shape, so, forexample, in some cases, the jacket body 101 is made of a castingmaterial of a 4000 series aluminum alloy, and a member having arelatively simple shape such as the sealing body 102 is made of anexpansible material of a 1000 series aluminum alloy. Thus, in somecases, a liquid-cooling jacket is manufactured by joining members madeof different kinds of aluminum alloys together. In such cases, ingeneral, the jacket body 101 has a higher hardness than the sealing body102. Hence, in a case where friction stir welding is performed in such amanner as that shown in FIG. 16 , the material resistance to thestirring pin FD2 to receive from the jacket body 101 is larger than thatto receive from the sealing body 102. As the result, it is difficult tostir different kinds of materials with good balance by the stirring pinFD2 of the rotary tool FD, so that there exists a problem that a cavitydefect is caused in a plasticized region formed by joining to reduce thejoint strength.

Further, after a liquid-cooling jacket is manufactured, in some cases,quality control of the liquid-cooling jacket is performed, for example,by ultrasonic flaw detection. In this inspection, the presence orabsence of poor joining can be detected by the ultrasonic flawdetection. However, there is a problem that it is not possible to knowwhere the rotary tool has passed.

From such a view point, it is an object of the present invention toprovide a method for manufacturing a liquid-cooling jacket and afriction stir welding method, the methods being capable of appropriatelyjoining different kinds of aluminum alloys and knowing where the rotarytool has passed.

Solution to Problem

In order to solve the problem, the present invention is characterized bya method for manufacturing a liquid-cooling jacket, in which a jacketbody provided with a bottom portion and a peripheral wall portion risingfrom a peripheral edge of the bottom portion, and a sealing body to sealan opening portion of the jacket body are friction stir welded, whereinthe jacket body is made of a material harder than the sealing body,wherein a rotary tool used for friction stirring is provided with a baseside pin and a tip side pin, and wherein a taper angle of the base sidepin is larger than a taper angle of the tip side pin, the base side pinhas a stepwise pin stepped portion on an outer circumferential facethereof, and an outer circumferential face of the tip side pin isinclined to have a smaller diameter with increasing distance toward atip thereof, the method comprising: a preparation process in which aperipheral wall stepped portion having a step bottom face and a stepside face is formed along an inner peripheral edge of the peripheralwall portion, the step side face rising from the step bottom face towardthe opening portion; a placing process in which by placing the sealingbody on the jacket body, a first butted portion is formed so that thestep side face of the peripheral wall stepped portion and an outerperipheral side face of the sealing body are butted against each other,and a second butted portion is formed so that the step bottom faceoverlaps with a back face of the sealing body; a primary joining processin which a coarse portion having a predetermined width is formed in thevicinity of the step side face within a plasticized region while therotary tool is being moved one round along the first butted portion toperform friction stirring in a state that the tip of the tip side pin ofthe rotary tool being rotated is inserted to the same depth as orslightly deeper than the step bottom face and the outer circumferentialface of the base side pin is in contact with a front face of the sealingbody and the tip side pin is slightly in contact with at least an upperportion of the jacket body; and an inspection process in which a passedposition of the tip side pin is specified by performing, after theprimary joining process, a flaw detection to detect the coarse portion.

According to this manufacturing method, the metal of the sealing body inthe first butted portion is mainly stirred to be plastically fluidizedbecause of the frictional heat between the sealing body and the tip sidepin, so that the step side face and an outer peripheral side face of thesealing body can be joined together in the first butted portion.Further, since friction stirring is performed in a state that the outercircumferential face of the base side pin is in contact with the frontface of the sealing body and the tip side pin is slightly in contactwith at least the upper portion of the step side face of the jacketbody, metal mixing into the sealing body from the jacket body can bereduced as much as possible while ensuring the joint strength. Hereby,the metal of the sealing body is mainly frictionally stirred in thefirst butted portion, so that lowering of the joint strength can besuppressed.

Further, since the tip side pin is inserted to the same depth as orslightly deeper than the step bottom face, metal mixing into the sealingbody from the jacket body can be reduced as much as possible whileenhancing the joint strength of the second butted portion. Furthermore,by deliberately forming the coarse portion having the predeterminedwidth, the passed position of the tip side pin can be detected throughflaw detection. Hereby, the quality control work can be more easilyperformed.

Further, the present invention is characterized by a method formanufacturing a liquid-cooling jacket, in which a jacket body providedwith a bottom portion and a peripheral wall portion rising from aperipheral edge of the bottom portion, and a sealing body to seal anopening portion of the jacket body are friction stir welded, wherein thejacket body is made of a material harder than the sealing body, whereina rotary tool used for friction stirring is provided with a base sidepin and a tip side pin, and wherein a taper angle of the base side pinis larger than a taper angle of the tip side pin, the base side pin hasa stepwise pin stepped portion on an outer circumferential face thereof,and an outer circumferential face of the tip side pin is inclined tohave a smaller diameter with increasing distance toward a tip thereof,the method comprising: a preparation process in which a peripheral wallstepped portion having a step bottom face and a step side face is formedalong an inner peripheral edge of the peripheral wall portion, the stepside face rising from the step bottom face toward the opening portion,and the sealing body is formed to have a thickness larger than a heightdimension of the step side face of the peripheral wall stepped portion;a placing process in which by placing the sealing body on the jacketbody, a first butted portion is formed so that the step side face of theperipheral wall stepped portion and an outer peripheral side face of thesealing body are butted against each other, and a second butted portionis formed so that the step bottom face overlaps with a back face of thesealing body; a primary joining process in which a coarse portion havinga predetermined width is formed in the vicinity of the step side facewithin a plasticized region while the rotary tool is being moved oneround along the first butted portion to perform friction stirring in astate that the tip of the tip side pin of the rotary tool being rotatedis inserted to the same depth as or slightly deeper than the step bottomface and the outer circumferential face of the base side pin is incontact with a front face of the sealing body and the tip side pin isslightly in contact with at least an upper portion of the jacket body;and an inspection process in which a passed position of the tip side pinis specified by performing, after the primary joining process, a flawdetection to detect the coarse portion.

According to this manufacturing method, the metal of the sealing body inthe first butted portion is mainly stirred to be plastically fluidizedbecause of the frictional heat between the sealing body and the tip sidepin, so that the step side face and an outer peripheral side face of thesealing body can be joined together in the first butted portion.Further, since friction stirring is performed in a state that the outercircumferential face of the base side pin is in contact with the frontface of the sealing body and the tip side pin is slightly in contactwith at least the upper portion of the step side face of the jacketbody, metal mixing into the sealing body from the jacket body can bereduced as much as possible while ensuring the joint strength. Hereby,the metal of the sealing body is mainly frictionally stirred in thefirst butted portion, so that lowering of the joint strength can besuppressed.

Further, since the tip side pin is inserted to the same depth as orslightly deeper than the step bottom face, metal mixing into the sealingbody from the jacket body can be reduced as much as possible whileenhancing the joint strength of the second butted portion. Furthermore,by deliberately forming the coarse portion having the predeterminedwidth, the passed position of the tip side pin can be detected throughflaw detection. Hereby, the quality control work can be more easilyperformed. Metal shortage of the joined portion can be prevented byenlarging the thickness of the sealing body.

Furthermore, the present invention is characterized by a method formanufacturing a liquid-cooling jacket, in which a jacket body providedwith a bottom portion and a peripheral wall portion rising from aperipheral edge of the bottom portion, and a sealing body to seal anopening portion of the jacket body are friction stir welded, wherein thejacket body is made of a material harder than the sealing body, whereina rotary tool used for friction stirring is provided with a base sidepin and a tip side pin, and wherein a taper angle of the base side pinis larger than a taper angle of the tip side pin, the base side pin hasa stepwise pin stepped portion on an outer circumferential face thereof,and an outer circumferential face of the tip side pin is inclined tohave a smaller diameter with increasing distance toward a tip thereof,the method comprising: a preparation process in which a peripheral wallstepped portion having a step bottom face and a step side face is formedalong an inner peripheral edge of the peripheral wall portion, the stepside face obliquely rising from the step bottom face toward the openingportion to spread, and the sealing body is formed to have a thicknesslarger than a height dimension of the step side face of the peripheralwall stepped portion; a placing process in which by placing the sealingbody on the jacket body, a first butted portion is formed to have a gapbetween the step side face of the peripheral wall stepped portion and anouter peripheral side face of the sealing body, and a second buttedportion is formed so that the step bottom face overlaps with a back faceof the sealing body; a primary joining process in which a coarse portionhaving a predetermined width is formed in the vicinity of the step sideface within a plasticized region while the rotary tool is being movedone round along the first butted portion to perform friction stirring ina state that the tip of the tip side pin of the rotary tool beingrotated is inserted to the same depth as or slightly deeper than thestep bottom face and the outer circumferential face of the base side pinis in contact with a front face of the sealing body and the tip side pinis slightly in contact with at least an upper portion of the jacketbody; and an inspection process in which a passed position of the tipside pin is specified by performing, after the primary joining process,a flaw detection to detect the coarse portion.

According to this manufacturing method, the metal of the sealing body inthe first butted portion is mainly stirred to be plastically fluidizedbecause of the frictional heat between the sealing body and the tip sidepin, so that the step side face and an outer peripheral side face of thesealing body can be joined together in the first butted portion.Further, since friction stirring is performed in a state that the outercircumferential face of the base side pin is in contact with the frontface of the sealing body and the tip side pin is slightly in contactwith at least the upper portion of the step side face of the jacketbody, metal mixing into the sealing body from the jacket body can bereduced as much as possible while ensuring the joint strength. Hereby,the metal of the sealing body is mainly frictionally stirred in thefirst butted portion, so that lowering of the joint strength can besuppressed.

Further, since the tip side pin is inserted to the same depth as orslightly deeper than the step bottom face, metal mixing into the sealingbody from the jacket body can be reduced as much as possible whileenhancing the joint strength of the second butted portion. Furthermore,by deliberately forming the coarse portion having the predeterminedwidth, the passed position of the tip side pin can be detected throughflaw detection. Hereby, the quality control work can be more easilyperformed. Further, by forming both of the outer circumferential face ofthe tip side pin and the step side face to be inclined, it can beavoided that the tip side pin and the step side face largely come intocontact with each other. Furthermore, metal shortage of the joinedportion can be prevented by enlarging the thickness of the sealing body.

It is preferable that the sealing body is made of an aluminum wroughtalloy material and the jacket body is made of an aluminum alloy castingmaterial.

It is preferable that the rotary tool is rotated clockwise in a casewhere the tip side pin of the rotary tool has a spiral groove in theouter circumferential face thereof, the spiral groove beingcounterclockwise with increasing distance from a base toward the tipthereof, and that the rotary tool is rotated counterclockwise in a casewhere the tip side pin of the rotary tool has a spiral groove in theouter circumferential face thereof, the spiral groove being clockwisewith increasing distance from a base toward the tip thereof.

Hereby, the plastically fluidized metal is led toward the tip side ofthe tip side pin through the spiral groove, so that the occurrence ofburrs can be reduced.

It is preferable that in the primary joining process, a rotationaldirection and an advancing direction of the rotary tool are set so thatwithin the plasticized region to be formed at a moving trace of therotary tool, a jacket body side is an advancing side and a sealing bodyside is a retreating side.

Hereby, the jacket body side is set to be an advancing side and thestirring action around the first butted portion by the tip side pin isenhanced, so that rising of the temperature at the first butted portionis expected, and the step side face and the outer peripheral side faceof the sealing body can be more firmly joined together at the firstbutted portion.

Furthermore, the present invention is characterized by a friction stirwelding method in which a first member and a second member are joinedtogether with use of a rotary tool, wherein the first member is made ofa material harder than the second member, wherein the rotary tool usedfor friction stirring is provided with a base side pin and a tip sidepin, and wherein a taper angle of the base side pin is larger than ataper angle of the tip side pin, the base side pin has a stepwise pinstepped portion on an outer circumferential face thereof, and an outercircumferential face of the tip side pin is inclined to have a smallerdiameter with increasing distance toward a tip thereof, the methodcomprising: a preparation process in which a step portion having a stepbottom face and a step side face rising from the step bottom face isformed in the first member; a placing process in which by placing thesecond member on the first member, a first butted portion is formed sothat the step side face of the step portion and a side face of thesecond member are butted against each other, and a second butted portionis formed so that the step bottom face overlaps with a back face of thesecond member; a primary joining process in which a coarse portionhaving a predetermined width is formed in the vicinity of the step sideface within a plasticized region while the rotary tool is being movedone round along the first butted portion to perform friction stirring ina state that the tip of the tip side pin of the rotary tool beingrotated is inserted to the same depth as or slightly deeper than thestep bottom face and the outer circumferential face of the base side pinis in contact with a front face of the second member and the tip sidepin is slightly in contact with at least an upper portion of the firstmember; and an inspection process in which a passed position of the tipside pin is specified by performing, after the primary joining process,a flaw detection to detect the coarse portion.

Advantageous Effects of Invention

According to the method for manufacturing a liquid-cooling jacket andthe friction stir welding method according to the present invention,different kinds of metals can be appropriately joined together and it ispossible to know where the rotary tool has passed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a side view showing a rotary tool according to one embodimentof the present invention.

FIG. 2 is an enlarged sectional view of the rotary tool.

FIG. 3 is a sectional view showing a first modification of the rotarytool.

FIG. 4 is a sectional view showing a second modification of the rotarytool.

FIG. 5 is a sectional view showing a third modification of the rotarytool.

FIG. 6 is a perspective view showing a preparation process of a methodfor manufacturing a liquid-cooling jacket according to a firstembodiment of the present invention.

FIG. 7 is a cross sectional view showing a placing process of the methodfor manufacturing a liquid-cooling jacket according to the firstembodiment.

FIG. 8 is a perspective view showing a primary joining process of themethod for manufacturing a liquid-cooling jacket according to the firstembodiment.

FIG. 9 is a cross sectional view showing the primary joining process ofthe method for manufacturing a liquid-cooling jacket according to thefirst embodiment.

FIG. 10 is a cross sectional view showing the liquid-cooling jacketafter the primary joining process of the method for manufacturing aliquid-cooling jacket according to the first embodiment is finished.

FIG. 11 is a plan view showing an inspection process of the method formanufacturing a liquid-cooling jacket according to the first embodiment.

FIG. 12 is a view showing an example that a tip side pin is inserted ina position where an outer circumferential face of the tip side pin isaway from a step side face.

FIG. 13 is a view showing an example that the tip side pin is insertedin a position where the outer circumferential face of the tip side pinis in contact with the step side face to a large extent.

FIG. 14 is a perspective view showing a preparation process of a methodfor manufacturing a liquid-cooling jacket according to a secondembodiment.

FIG. 15 is a cross sectional view showing a primary joining process ofthe method for manufacturing a liquid-cooling jacket according to thesecond embodiment.

FIG. 16 is a cross sectional view showing a conventional method formanufacturing a liquid-cooling jacket.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will be described with referenceto the drawings where appropriate. First, a rotary tool which is used ina method for manufacturing a liquid-cooling jacket according to thepresent embodiment will be described. The rotary tool is a tool to beused for friction stir welding. As shown in FIG. 1 , a rotary tool F ismade of, for example, tool steel, and is mainly formed of a base shaftF1, a base side pin F2 and a tip side pin F3. The base shaft F1 has acylindrical shape and is a portion to be connected to a spindle of afriction stir device.

The base side pin F2 is continuous with the base shaft F1, and has atapered shape in which a diameter of the base side pin F2 is reducedtoward a tip of the base side pin F2. The base side pin F2 has afrustoconical shape. A taper angle A of the base side pin F2 can beappropriately set, and is, for example, 135 to 160°. In a case where thetaper angle A is less than 135° or greater than 160°, the roughness ofthe joined surface after friction stirring becomes larger. Further, thetaper angle A is larger than a taper angle B of the tip side pin F3 tobe described later. As shown in FIG. 2 , the base side pin F2 has astepwise pin stepped portion F21 on an outer circumferential face of thebase side pin F2 along the whole height of the base side pin F2. The pinstepped portion F21 is spirally formed in a clockwise orcounterclockwise direction. In other words, the pin stepped portion F21is spiral in a plan view and stepwise in a side view. In this firstembodiment, the pin stepped portion F21 is set to be counterclockwisefrom a base side toward the tip side because the rotary tool F isrotated clockwise.

In a case where the rotary tool F is rotated counterclockwise, it ispreferable that the pin stepped portion F21 is set to be clockwise fromthe base side toward the tip side. This allows plastically fluidizedmaterial to be guided toward the tip side by the pin stepped portionF21, so that the amount of metal to be leaked out of metal members to bejoined together can be reduced. The pin stepped portion F21 is formed ofa step bottom face F21 a and a step side face F21 b. A distance(horizontal distance) X1 between adjacent vertices F21 c and F21 c ofthe pin stepped portion F21 is appropriately set according to a heightY1 of the step side face F21 b and a step angle C to be described later.

The height Y1 of the step side face F21 b may be appropriately set, andis set, for example, to be 0.1 to 0.4 mm. In a case where the height Y1is less than 0.1 mm, the roughness of the joined surface becomes larger.On the other hand, in a case where the height Y1 is greater than 0.4 mm,the roughness of the joined surface tends to become larger and thenumber of effective step portions (the number of the pin steppedportions F21 being in contact with the metal members to be joined) isreduced.

The step angle C defined by the step bottom face F21 a and the step sideface F21 b may be set appropriately, and is set to, for example, 85 to120°. The step bottom face F21 a is parallel to a horizontal plane inthis embodiment. The step bottom face F21 a may be inclined from theaxis of the tool toward the outer circumferential face in the range of -5° to 15° with respect to the horizontal plane. A minus means lower withrespect to the horizontal plane, and a plus means upper with respect tothe horizontal plane. The distance X1, the height Y1 of the step sideface F21 b, the step angle C and the angle of the step bottom face F21 awith respect to the horizontal plane are appropriately set so that whenfriction stirring is performed, the roughness of the joined surface canbe reduced by pressing plastically fluidized material with the stepbottom face F21 a while the plastically fluidized material does not stayinside the pin stepped portion F21 nor adhere to the pin stepped portionF21 and the plastically fluidized material goes outside.

As shown in FIG. 1 , the tip side pin F3 is formed continuously to thebase side pin F2. The tip side pin F3 has a frustoconical shape. The tipside pin F3 has a flat face F4 at the tip thereof. The flat face F4 isnormal to the rotational axis. The taper angle B of the tip side pin F3is smaller than the taper angle A of the base side pin F2. As shown inFIG. 2 , the tip side pin F3 has a spiral groove F31 on the outercircumferential face thereof. The spiral groove F31 may be eitherclockwise or counterclockwise. In this first embodiment, the spiralgroove F31 is formed to be counterclockwise from the base side towardthe tip side because the rotary tool F is rotated clockwise.

It should be noted that, in a case where the rotary tool F is rotatedcounterclockwise, it is preferable that the spiral groove F31 is formedto be clockwise from the base side toward the tip side. This allowsplastically fluidized material to be led toward the tip side through thespiral groove F31, so that the amount of metal overflowing outside themetal members to be joined can be reduced. The spiral groove F31 isformed of a spiral bottom face F31 a and a spiral side face F31 b. Thedistance (horizontal distance) between adjacent vertices F31 c and F31 cof the spiral groove F31 is set to a length X2. A height of the spiralside face F31 b is set to a height Y2. A spiral angle D defined by thespiral bottom face F31 a and the spiral side face F31 b is set, forexample, to 45 to 90°. The spiral groove F31 has a role of leadingplastically fluidized material toward the tip side as well as a role ofrising frictional heat by coming into contact with the metal members tobe joined. The rotary tool F may be attached to a robot arm having a tipend equipped with a rotary drive means such as a spindle unit.

The design of the rotary tool F can be appropriately changed. FIG. 3 isa side view showing a first modification of the rotary tool of thepresent invention. As shown in FIG. 3 , in the rotary tool FA accordingto the first modification, the step angle C defined by the step bottomface F21 a and the step side face F21 b of the pin stepped portion F21is 85°. The step bottom face F21 a is parallel to the horizontal plane.In this way, the step bottom face F21 a is parallel to the horizontalplane and the step angle C may be an acute angle in a range in whichplastically fluidized material can be led to the outside without stayingin nor adhering to the inside of the pin stepped portion F21 whenfriction stirring is performed.

FIG. 4 is a side view showing a second modification of the rotary toolof the present invention. As shown in FIG. 4 , in the rotary tool FBaccording to the second modification, the step angle C of the pinstepped portion F21 is 115°. The step bottom face F21 a is parallel tothe horizontal plane. In this way, the step bottom face F21 a may beparallel to the horizontal plane and the step angle C may be an obtuseangle in a range of functioning as the pin stepped portion F21.

FIG. 5 is a side view showing a third modification of the rotary tool ofthe present invention. As shown in FIG. 5 , in the rotary tool FCaccording to the third modification, the step bottom face F21 a isinclined upward from the axis of the tool toward the outercircumferential face by 10° with respect to the horizontal plane. Thestep side face F21 b is parallel to the vertical plane. In this way, thetool may be formed in such a form that the step bottom face F21 a isinclined upward from the axis of the tool toward the outercircumferential face with respect to the horizontal plane in a range inwhich plastically fluidized material can be pressed when frictionstirring is performed. Each of the first to the third modifications ofthe rotary tool has the same advantageous effects as those of thefollowing embodiments.

In this embodiment, the rotary tool F is attached to the friction stirdevice capable of moving in the horizontal directions as well as in thevertical directions. It should be noted that the rotary tool F may beattached to a robot arm having a tip end equipped with a rotary drivemeans such as a spindle unit.

First Embodiment

A method for manufacturing a liquid-cooling jacket according to anembodiment of the present invention will be described in detail withreference to the drawings. As shown in FIG. 6 , the method formanufacturing a liquid-cooling jacket 1 according to the embodiment ofthe present invention is a method where the liquid-cooling jacket 1 ismanufactured by performing friction stir welding to a jacket body 2 anda sealing body 3. The liquid-cooling jacket 1 includes the sealing body3, on which a heating element (not shown) is placed and inside which afluid is allowed to flow to exchange heat with the heating element. Itshould be noted that, hereinafter, a “front face” means the faceopposite to a “back face”.

The method for manufacturing a liquid-cooling jacket according to thisembodiment includes a preparation process, a placing process, a primaryjoining process and an inspection process. The preparation process is aprocess to prepare the jacket body 2 and the sealing body 3. The jacketbody 2 is mainly composed of a bottom portion 10 and a peripheral wallportion 11. The jacket body 2 is made of a material mainly containing afirst aluminum alloy. The first aluminum alloy is, for example, analuminum alloy casting material such as JISH5302 ADC12 (based onAl—Si—Cu). The jacket body 2 is made of an aluminum alloy as an examplein this embodiment, but may be made of another metal capable of beingfrictionally stirred.

As shown in FIG. 6 , the bottom portion 10 is a plate-like member havinga rectangular shape in a plan view. The peripheral wall portion 11 is awall portion rising from the peripheral edge portion of the bottomportion 10 and having a rectangular frame shape. A peripheral wallstepped portion 12 is formed at an inner peripheral edge of theperipheral wall portion 11. The peripheral wall stepped portion 12 iscomposed of a step bottom face 12 a and a step side face 12 b risingfrom the step bottom face 12 a. As shown in FIG. 7 , the step side face12 b inclines to spread toward the outside with increasing distance fromthe step bottom face 12 a and toward an opening portion. An inclinationangle β of the step side face 12 b with respect to the vertical planemay be appropriately set, and is set to, for example, 3° to 30° withrespect to the vertical plane. A recessed portion 13 is defined by thebottom portion 10 and the peripheral wall portion 11. Here, the verticalplane is defined as a plane composed of an advancing vector of therotary tool F and a vertical vector.

The sealing body 3 is a plate-like member to seal the opening portion ofthe jacket body 2. The sealing body 3 has a size capable of being placedon the peripheral wall stepped portion 12. A thickness of the sealingbody 3 is larger than a height dimension of the step side face 12 b. Thethickness of the sealing body 3 is appropriately set so that a joinedportion does not fall in shortage of metal when the primary joiningprocess to be described later is performed. The sealing body 3 is madeof a material mainly containing a second aluminum alloy. The secondaluminum alloy has a hardness lower than the first aluminum alloy. Thesecond aluminum alloy is, for example, an aluminum wrought alloymaterial such as JIS A1050, A1100, A6063. The sealing body 3 is made ofan aluminum alloy as an example in this embodiment, but may be made ofanother metal capable of being frictionally stirred. It should be notedthat the hardness in this description refers to Brinell hardness, whichcan be measured by a method in conformity with JIS Z 2243.

The placing process is a process to place the sealing body 3 on thejacket body 2 as shown in FIG. 7 . In the placing process, a back face 3b of the sealing body 3 is placed on the step bottom face 12 a. The stepside face 12 b and an outer peripheral side face 3 c of the sealing body3 are butted against each other to form a first butted portion J1. Thefirst butted portion J1 may also include a case where two members arebutted against each other to have an approximately V-shaped gap in crosssection like this embodiment. Furthermore, the step bottom face 12 aoverlaps with the back face 3 b of the sealing body 3 to form a secondbutted portion J2.

As shown in FIGS. 8 and 9 , the primary joining process is a processwhere friction stir welding is performed to the jacket body 2 and thesealing body 3 with use of the rotary tool F being rotated while movingthe rotary tool F one round around the sealing body 3.

As shown in FIG. 8 , when friction stirring is performed with use of therotary tool F, the tip side pin F3 being rotated clockwise is insertedin the sealing body 3 and moved in a state that the outercircumferential face of the base side pin F2 is in contact with thefront face 3 a of the sealing body 3. The metal frictionally stirred ishardened, so that a plasticized region W1 is formed at a moving trace ofthe rotary tool F. In this embodiment, the tip side pin F3 is insertedat a start position Sp set on the sealing body 3 and the rotary tool Fis moved clockwise relative to the sealing body 3.

As shown in FIG. 9 , in the primary joining process, friction stirringis performed in a state that the rotation axis X of the rotary tool F isparallel to the vertical line (vertical plane). As shown in FIG. 7 , theinclination angle β of the step side face 12 b is set smaller than theinclination angle α of the outer circumferential face of the tip sidepin F3. In the primary joining process, the setting is made so that alower portion of the outer circumferential face of the tip side pin F3is not in contact with the step side face 12 b of the peripheral wallstepped portion 12 in a state that the outer circumferential face of thebase side pin F2 is in contact with the front face 3 a of the sealingbody 3 and an upper portion of the outer circumferential face of the tipside pin F3 is slightly brought in contact with an upper portion of thestep side face 12 b of the peripheral wall stepped portion 12. The flatface F4 of the tip side pin F3 may be inserted to the same heightposition as the step bottom face 12 a of the peripheral wall steppedportion 12, but in this embodiment, the flat face F4 is inserted to aslightly deeper position than the step bottom face 12 a of theperipheral wall stepped portion 12. In the primary joining process, therotary tool F is made to leave the jacket body 2 and the sealing body 3after the rotary tool F is moved one round around the sealing body 3 tooverlap a beginning and an end of the plasticized region W1.

As shown in FIG. 10 , by the primary joining process, the plasticizedregion W1 is formed at the moving trace of the rotary tool F and acoarse portion Z is formed at a region which is in the lower portion ofthe plasticized region W1 and in the vicinity of the inside of the stepside face 12 b. The coarse portion Z is a region in which theplastically fluidized material has not been sufficiently stirred and thedensity of the plastically fluidized material is coarser than the otherregion. The coarse portion Z is formed continuously or intermittently inthe length direction of the plasticized region W1.

As shown in FIG. 11 , the inspection process is a process to perform aflaw detection for a liquid-cooling jacket 1. In the inspection process,an ultrasonic flaw detection device (for example, ultrasonic imagingdevice (SAT) manufactured by Hitachi High-Teck GLOBAL) is used. A hollowportion U of the liquid-cooling jacket 1 in an inspection result screenR in FIG. 11 is shown in another color. Further, the coarse portion Z isshown around the hollow portion U in another color and in a frame shapewith broken lines. That is, it can be judged that the rotary tool F haspassed the entire periphery of the sealing body 3 by displaying thecoarse portion Z on the inspection result screen R. The region betweenthe hollow portion U and the coarse portion Z is an area correspondingto the plasticized region W1.

It is preferable that the width Zw of the coarse portion Z is 400 µm orless, more preferably 300 µm or less, and still more preferably 200 µmor less. In a case where the width Zw of the coarse portion Z is morethan 400 µm, there is a concern of poor joint strength of the firstbutted portion J1. In other words, in the case where the width Zw of thecoarse portion Z is 400 µm or less, sufficient joint strength isobtained. On the other hand, it is preferable that the width Zw of thecoarse portion Z is 100 µm or more. In a case where the width Zw of thecoarse portion Z is less than 100 µm, there is a concern that the coarseportion Z is not shown on the inspection result screen R by theultrasonic flaw detection device.

As shown in FIG. 9 , in the primary joining process, the ratio of aregion where the outer circumferential face of the tip side pin F3 is incontact with the step side face 12 b and the other region where theouter circumferential face of the tip side pin F3 is not in contact withthe step side face 12 b is about 2:8 in this embodiment. The ratio maybe appropriately set in a range where the jacket body 2 and the sealingbody 3 are joined together with a desired strength and the coarseportion Z having the above-described predetermined width is formed. Inother words, the inclination angle α of the outer circumferential faceof the tip side pin F3, the inclination angle β of the step side face 12b of the peripheral wall stepped portion 12, and the position (positionin a width direction) of the rotation axis X of the tip side pin F3 maybe appropriately set in a range where the jacket body 2 and the sealingbody 3 are joined together with a desired strength and the coarseportion Z having the above-described predetermined width is formed.

As shown in FIG. 12 , it is preferable that the tip side pin F3 isbrought into contact at least with the upper portion of the step sideface 12 b. This is because if the outer circumferential face of the tipside pin F3 is away from the step side face 12 b, the jacket body 2 andthe sealing body 3 may not be joined together or the joint strengththereof may be reduced. Further, as shown in FIG. 13 , in a case wherethe contacting margin between the tip side pin F3 and the step side face12 b is larger, more metal of the jacket body 2 having a higher hardnessflows toward the sealing body 3 having a lower hardness. Consequently,the stirring balance between the jacket body 2 and the sealing body 3 ispoor, so that there is a concern that the joint strength decreases.Furthermore, in the vicinity of the step bottom face 12 a, in a casewhere the outer circumferential face of the tip side pin F3 and the stepside face 12 b are too close and also in a case where they are too far,it is difficult to form the coarse portion Z having the above-describedpredetermined width.

According to the method for manufacturing a liquid-cooling jacketaccording to this embodiment described in the above, the metal of thesealing body 3 at the first butted portion J1 is mainly frictionallystirred to be plastically fluidized because of the frictional heatbetween the tip side pin F3 and the sealing body 3, so that the stepside face 12 b and the outer peripheral side face 3 c of the sealingbody 3 can be joined together at the first butted portion J1. Further,since friction stirring is performed in a state that the outercircumferential face of the base side pin F2 is in contact with thefront face 3 a of the sealing body 3 and the tip side pin F3 is slightlyin contact with at least an upper portion of the step side face 12 b ofthe jacket body 2, it is possible to reduce metal mixing from the jacketbody 2 to the sealing body 3 as much as possible while ensuring thejoint strength. Accordingly, since the metal of the sealing body 3 ismainly frictionally stirred at the first butted portion J1, lowering ofthe joint strength can be suppressed.

Further, since the tip side pin F3 is inserted to the same depth as thestep bottom face 12 a or slightly deeper than that, it is possible toreduce metal mixing from the jacket body 2 to the sealing body 3 as muchas possible while enhancing the joint strength at the second buttedportion J2. Further, by deliberately forming the coarse portion Z havingthe predetermined width, the passed position of the tip side pin F3 canbe detected by flaw detection. Hereby, quality control work can be moreeasily performed. Furthermore, by forming the sealing body 3 to have athickness larger than the step side face 12 b, the joined portion can beprevented from falling in metal shortage.

In the primary joining process, a rotational direction and an advancingdirection of the rotary tool F may be appropriately set. In thisembodiment, the rotational direction and the advancing direction of therotary tool F have been set so that the jacket body 2 side is anadvancing side and the sealing body 3 side is a retreating side withinthe plasticized region W1 to be formed at the moving trace of the rotarytool F. This enhances the stirring action by the tip side pin F3 aroundthe first butted portion J1, so that rising of the temperature at thefirst butted portion J1 is expected, and the step side face 12 b and theouter peripheral side face 3 c of the sealing body 3 can be more firmlyjoined together at the first butted portion J1.

It should be noted that, an advancing side (Shear side) is a side wherethe relative speed of the outer periphery of the rotary tool relative toa portion to be joined takes a value that an advancing speed is added toa tangential speed at the outer periphery of the rotary tool. On theother hand, a retreating side (Flow side) is a side where the relativespeed of the rotary tool relative to a portion to be joined is loweredsince the rotary tool is rotated in the direction opposite to theadvancing direction of the rotary tool.

The first aluminum alloy of the jacket body 2 has a hardness harder thanthe second aluminum alloy of the sealing body 3. This can enhance theendurance of the liquid-cooling jacket 1. Further, it is preferable thatthe first aluminum alloy of the jacket body 2 is an aluminum alloycasting material and the second aluminum alloy of the sealing body 3 isan aluminum wrought alloy material. In a case where the first aluminumalloy is, for example, the aluminum alloy casting material based onAl—Si—Cu such as JISH5302 ADC12, castability, strength and machinabilityof the jacket body 2 can be enhanced. Furthermore, in a case where thesecond aluminum alloy is, for example, a material of JIS A1000 series orA6000 series, processing ability and thermal conductivity can beenhanced.

For example, the thickness of the sealing body 3 is set larger than theheight dimension of the step side face 12 b in this embodiment, but bothmay be the same with each other. Further, the step side face 12 b maynot be inclined and be formed perpendicular to the step bottom face 12a.

In the above embodiment, the method for manufacturing a liquid-coolingjacket that is formed by joining the jacket body and the sealing bodyhas been described as an example, but the present invention is notlimited to this specific embodiment. Although not shown in the drawings,the present invention is applicable, without being limited to a specificshape of the liquid-cooling jacket, to friction stir welding performedwhen a first member having a step portion and a second member to beplaced on the step portion are joined together.

Second Embodiment

Next, a method for manufacturing a liquid-cooling jacket according to asecond embodiment of the present invention will be described. As shownin FIGS. 14 and 15 , the second embodiment differs from the firstembodiment in that columnar supports 15 of a jacket body 2A and asealing body 3A are joined together. In this embodiment, a preparationprocess, a placing process, a primary joining process, and an inspectionprocess are performed. The primary joining process includes a firstprimary joining process and a second primary joining process. In thisembodiment, differences from the first embodiment will be mainlydescribed.

In the preparation process, the jacket body 2A and the sealing body 3Aare prepared. The jacket body 2A is provided with a bottom portion 10, aperipheral wall portion 11, and a plurality of columnar supports 15(four columnar supports in this embodiment). Each columnar support 15rises from the bottom portion 10 and has a columnar shape. Each columnarsupport 15 is provided with a projection portion 16 tapered to have asmaller diameter with increasing distance toward a tip thereof at thetop thereof. Since the projection portion 16 is provided, a columnarsupport stepped portion 17 is formed on the top side of the columnarsupport 15. The columnar support stepped portion 17 is composed of astep bottom face 17 a and a step side face 17 b inclined toward the axisthereof from the step bottom face 17 a. The sealing body 3A has holeportions 4 formed at positions corresponding to the columnar supports15. Each hole portion 4 has such a size that a corresponding projectionportion 16 can be inserted therein.

The placing process is a process in which the sealing body 3A is placedon the jacket body 2A. This process forms a first butted portion J1 likethe first embodiment. Further, as shown in FIG. 15 , the step side face17 b of the columnar support stepped portion 17 and a hole wall 4 a ofthe hole portion 4 are butted against each other to form a third buttedportion J3. Furthermore, the step bottom face 17 a of the columnarsupport stepped portion 17 overlaps with a back face 3 b of the sealingbody 3A to form a fourth butted portion J4.

In the primary joining process, the first primary joining process inwhich the first butted portion J1 and the second butted portion J2 arejoined, and the second primary joining process in which the third buttedportion J3 and the fourth butted portion J4 are joined are performed.Description of the first primary joining process is omitted because thefirst primary joining process is the same as the primary joining processin the first embodiment.

As shown in FIG. 15 , in the second primary joining process, an upperportion of the outer circumferential face of the tip side pin F3 isslightly brought in contact with an upper portion of the step side face17 b of the columnar support stepped portion 17 and a lower portion ofthe outer circumferential face of the tip side pin F3 is not brought incontact with the step side face 17 b of the columnar support steppedportion 17. The outer circumferential face of the base side pin F2 iskept in contact with the front face 3 a of the sealing body 3A and thefront face 16 a of the projection portion 16. The tip side pin F3 isinserted so that the flat face F4 thereof is located at a positionslightly deeper than the step bottom face 17 a of the columnar supportstepped portion 17.

As shown in FIG. 15 , by performing the primary joining process, aplasticized region W2 is formed at a moving trace of the rotary tool F,and the coarse portion Z is formed in the outside vicinity of the stepside face 17 b in a lower portion of the plasticized region W2. Thecoarse portion Z is a portion in which the plastically fluidizedmaterial is not fully frictionally stirred and thus coarser than theother portions. The coarse portion Z is continuously or intermittentlyformed in the plasticized region W2. A forming method and formingconditions for the coarse portion Z are the same as that or those in thefirst embodiment.

This embodiment can attain similar effects to the first embodiment.Further, this embodiment can enhance the joint strength since thecolumnar supports 15 and the sealing body 3A are joined together.Furthermore, the moving trace of the rotary tool F around the columnarsupports 15 can be confirmed in the inspection process by forming thecoarse portion Z in the outside vicinity of the base side of each of theprojection portions 16 within the plasticized region W2.

REFERENCE SIGNS LIST

-   1 Liquid-cooling jacket-   2 Jacket body (First member)-   3 Sealing body (Second member)-   F Rotary tool-   F1 Base shaft-   F2 Base side pin-   F3 Tip side pin-   F4 Flat face-   J1 First butted portion-   J2 Second butted portion-   W1 Plasticized region-   Z Coarse portion

1-7. (canceled)
 8. A method for manufacturing a liquid-cooling jacket,in which a jacket body provided with a bottom portion and a peripheralwall portion rising from a peripheral edge of the bottom portion, and asealing body to seal an opening portion of the jacket body are frictionstir welded, wherein the jacket body is made of a material harder thanthe sealing body, wherein a rotary tool used for friction stirring isprovided with a base side pin and a tip side pin, and wherein a taperangle of the base side pin is larger than a taper angle of the tip sidepin, the base side pin has a stepwise pin stepped portion on an outercircumferential face thereof, and an outer circumferential face of thetip side pin is inclined to have a smaller diameter with increasingdistance toward a tip thereof, the method comprising: a preparationprocess in which a peripheral wall stepped portion having a step bottomface and a step side face is formed along an inner peripheral edge ofthe peripheral wall portion, the step side face rising from the stepbottom face toward the opening portion; a placing process in which byplacing the sealing body on the jacket body, a first butted portion isformed so that the step side face of the peripheral wall stepped portionand an outer peripheral side face of the sealing body are butted againsteach other, and a second butted portion is formed so that the stepbottom face overlaps with a back face of the sealing body; a primaryjoining process in which a coarse portion having a predetermined widthis formed in the vicinity of the step side face within a plasticizedregion while the rotary tool is being moved one round along the firstbutted portion to perform friction stirring in a state that the tip ofthe tip side pin of the rotary tool being rotated is inserted to thesame depth as or slightly deeper than the step bottom face and the outercircumferential face of the base side pin is in contact with a frontface of the sealing body and the tip side pin is slightly in contactwith at least an upper portion of the jacket body; and an inspectionprocess in which a passed position of the tip side pin is specified byperforming, after the primary joining process, a flaw detection todetect the coarse portion.
 9. The method for manufacturing aliquid-cooling jacket according to claim 8, wherein the sealing body ismade of an aluminum wrought alloy material and the jacket body is madeof an aluminum alloy casting material.
 10. The method for manufacturinga liquid-cooling jacket according to claim 8, wherein the rotary tool isrotated clockwise in a case where the tip side pin of the rotary toolhas a spiral groove in the outer circumferential face thereof, thespiral groove being counterclockwise with increasing distance from abase toward the tip thereof, and wherein the rotary tool is rotatedcounterclockwise in a case where the tip side pin of the rotary tool hasa spiral groove in the outer circumferential face thereof, the spiralgroove being clockwise with increasing distance from a base toward thetip thereof.
 11. The method for manufacturing a liquid-cooling jacketaccording to claim 8, wherein in the primary joining process, arotational direction and an advancing direction of the rotary tool areset so that within the plasticized region to be formed at a moving traceof the rotary tool, a jacket body side is an advancing side and asealing body side is a retreating side.
 12. A method for manufacturing aliquid-cooling jacket, in which a jacket body provided with a bottomportion and a peripheral wall portion rising from a peripheral edge ofthe bottom portion, and a sealing body to seal an opening portion of thejacket body are friction stir welded, wherein the jacket body is made ofa material harder than the sealing body, wherein a rotary tool used forfriction stirring is provided with a base side pin and a tip side pin,and wherein a taper angle of the base side pin is larger than a taperangle of the tip side pin, the base side pin has a stepwise pin steppedportion on an outer circumferential face thereof, and an outercircumferential face of the tip side pin is inclined to have a smallerdiameter with increasing distance toward a tip thereof, the methodcomprising: a preparation process in which a peripheral wall steppedportion having a step bottom face and a step side face is formed alongan inner peripheral edge of the peripheral wall portion, the step sideface rising from the step bottom face toward the opening portion, andthe sealing body is formed to have a thickness larger than a heightdimension of the step side face of the peripheral wall stepped portion;a placing process in which by placing the sealing body on the jacketbody, a first butted portion is formed so that the step side face of theperipheral wall stepped portion and an outer peripheral side face of thesealing body are butted against each other, and a second butted portionis formed so that the step bottom face overlaps with a back face of thesealing body; a primary joining process in which a coarse portion havinga predetermined width is formed in the vicinity of the step side facewithin a plasticized region while the rotary tool is being moved oneround along the first butted portion to perform friction stirring in astate that the tip of the tip side pin of the rotary tool being rotatedis inserted to the same depth as or slightly deeper than the step bottomface and the outer circumferential face of the base side pin is incontact with a front face of the sealing body and the tip side pin isslightly in contact with at least an upper portion of the jacket body;and an inspection process in which a passed position of the tip side pinis specified by performing, after the primary joining process, a flawdetection to detect the coarse portion.
 13. The method for manufacturinga liquid-cooling jacket according to claim 12, wherein the sealing bodyis made of an aluminum wrought alloy material and the jacket body ismade of an aluminum alloy casting material.
 14. The method formanufacturing a liquid-cooling jacket according to claim 12, wherein therotary tool is rotated clockwise in a case where the tip side pin of therotary tool has a spiral groove in the outer circumferential facethereof, the spiral groove being counterclockwise with increasingdistance from a base toward the tip thereof, and wherein the rotary toolis rotated counterclockwise in a case where the tip side pin of therotary tool has a spiral groove in the outer circumferential facethereof, the spiral groove being clockwise with increasing distance froma base toward the tip thereof.
 15. The method for manufacturing aliquid-cooling jacket according to claim 12, wherein in the primaryjoining process, a rotational direction and an advancing direction ofthe rotary tool are set so that within the plasticized region to beformed at a moving trace of the rotary tool, a jacket body side is anadvancing side and a sealing body side is a retreating side.
 16. Amethod for manufacturing a liquid-cooling jacket, in which a jacket bodyprovided with a bottom portion and a peripheral wall portion rising froma peripheral edge of the bottom portion, and a sealing body to seal anopening portion of the jacket body are friction stir welded, wherein thejacket body is made of a material harder than the sealing body, whereina rotary tool used for friction stirring is provided with a base sidepin and a tip side pin, and wherein a taper angle of the base side pinis larger than a taper angle of the tip side pin, the base side pin hasa stepwise pin stepped portion on an outer circumferential face thereof,and an outer circumferential face of the tip side pin is inclined tohave a smaller diameter with increasing distance toward a tip thereof,the method comprising: a preparation process in which a peripheral wallstepped portion having a step bottom face and a step side face is formedalong an inner peripheral edge of the peripheral wall portion, the stepside face obliquely rising from the step bottom face toward the openingportion to spread, and the sealing body is formed to have a thicknesslarger than a height dimension of the step side face of the peripheralwall stepped portion; a placing process in which by placing the sealingbody on the jacket body, a first butted portion is formed to have a gapbetween the step side face of the peripheral wall stepped portion and anouter peripheral side face of the sealing body, and a second buttedportion is formed so that the step bottom face overlaps with a back faceof the sealing body; a primary joining process in which a coarse portionhaving a predetermined width is formed in the vicinity of the step sideface within a plasticized region while the rotary tool is being movedone round along the first butted portion to perform friction stirring ina state that the tip of the tip side pin of the rotary tool beingrotated is inserted to the same depth as or slightly deeper than thestep bottom face and the outer circumferential face of the base side pinis in contact with a front face of the sealing body and the tip side pinis slightly in contact with at least an upper portion of the jacketbody; and an inspection process in which a passed position of the tipside pin is specified by performing, after the primary joining process,a flaw detection to detect the coarse portion.
 17. The method formanufacturing a liquid-cooling jacket according to claim 16, wherein thesealing body is made of an aluminum wrought alloy material and thejacket body is made of an aluminum alloy casting material.
 18. Themethod for manufacturing a liquid-cooling jacket according to claim 16,wherein the rotary tool is rotated clockwise in a case where the tipside pin of the rotary tool has a spiral groove in the outercircumferential face thereof, the spiral groove being counterclockwisewith increasing distance from a base toward the tip thereof, and whereinthe rotary tool is rotated counterclockwise in a case where the tip sidepin of the rotary tool has a spiral groove in the outer circumferentialface thereof, the spiral groove being clockwise with increasing distancefrom a base toward the tip thereof.
 19. The method for manufacturing aliquid-cooling jacket according to claim 16, wherein in the primaryjoining process, a rotational direction and an advancing direction ofthe rotary tool are set so that within the plasticized region to beformed at a moving trace of the rotary tool, a jacket body side is anadvancing side and a sealing body side is a retreating side.
 20. Afriction stir welding method in which a first member and a second memberare joined together with use of a rotary tool, wherein the first memberis made of a material harder than the second member, wherein the rotarytool used for friction stirring is provided with a base side pin and atip side pin, and wherein a taper angle of the base side pin is largerthan a taper angle of the tip side pin, the base side pin has a stepwisepin stepped portion on an outer circumferential face thereof, and anouter circumferential face of the tip side pin is inclined to have asmaller diameter with increasing distance toward a tip thereof, themethod comprising: a preparation process in which a step portion havinga step bottom face and a step side face rising from the step bottom faceis formed in the first member; a placing process in which by placing thesecond member on the first member, a first butted portion is formed sothat the step side face of the step portion and a side face of thesecond member are butted against each other, and a second butted portionis formed so that the step bottom face overlaps with a back face of thesecond member; a primary joining process in which a coarse portionhaving a predetermined width is formed in the vicinity of the step sideface within a plasticized region while the rotary tool is being movedone round along the first butted portion to perform friction stirring ina state that the tip of the tip side pin of the rotary tool beingrotated is inserted to the same depth as or slightly deeper than thestep bottom face and the outer circumferential face of the base side pinis in contact with a front face of the second member and the tip sidepin is slightly in contact with at least an upper portion of the firstmember; and an inspection process in which a passed position of the tipside pin is specified by performing, after the primary joining process,a flaw detection to detect the coarse portion.